This removes Printer's legacy behaviour of generating an ID for each
node as it gets printed. This old method meant that if new nodes were
added to or removed from a graph, every ID after the new/removed node
would change.
Now IDs are stable so it is easier to follow specific nodes through
multiple transformation passes in CodeGen.
TypeGraphParser parses a textual type graph, as emitted by Printer.
It also doubles as a way of ensuring that Printer displays all
information about a type graph, to aid with debugging.
Convert Flattener unit tests over to this new framework as a first step.
These aren't used for anything yet, but should be useful for stable IDs
when printing nodes before and after passes and for faster cycle
detection than the current map of pointers.
For std::vector and std::list, template parameters are not required to
be defined before they can be used. Delay sorting them until the end.
Also fix a CodeGen bug where we were defining typedefs in the middle of
the forward declarations. They only need to be defined when other types
are defined.
